mirror of
https://github.com/opentffoundation/opentf.git
synced 2025-12-19 17:59:05 -05:00
5fa35c5601
This introduces the concept of "backend aliases", which are alternative names that can be used to refer to a given backend. Each backend type has one canonical name and zero or more alias names. The "backend" block in the root module can specify either a canonical backend type or an alias, but internally OpenTofu will always track the backend type using its canonical name. In particular, the following are all true when the configuration specifies an alias instead of a canonical backend type: - The "tofu init" output includes a brief extra message saying which backend type OpenTofu actually used, because that is the name that we'd prioritize in our documentation and so an operator can use the canonical type to find the relevant docs when needed. - The .terraform/terraform.tfstate file that tracks the working directory's currently-initialized backend settings always uses the canonical backend type, and so it's possible to freely switch between aliases and canonical without "tofu init" thinking that a state migration might be needed. - Plan files similarly use the canonical backend type to track which backend was active when the plan was created, which doesn't have any significant user-facing purpose, but is consistent with the previous point since the settings in the plan file effectively substitute for the .terraform/terraform.tfstate file when applying a saved plan. - The terraform_remote_state data source in the provider terraform.io/builtin/terraform accepts both canonical and alias in its backend type argument, treating both as equivalent for the purpose of fetching the state snapshot for the configured workspace. The primary motivation for this new facility is to allow the planned "oracle_oci" backend to have an alias "oci" to allow writing configurations that are cross-compatible with HashiCorp Terraform, since that software has chosen to have unqualified OCI mean Oracle's system, whereas OpenTofu has previously established that unqualified OCI means "Open Container Initiative" in our ecosystem. In particular, this design makes it possible in principle to bring an existing Terraform configuration specifying backend "oci" over to OpenTofu without modifications, and then to optionally switch it to specifying backend "oracle-oci" at a later time without a spurious prompt to migrate state snapshots to the same physical location where they are already stored. This commit doesn't actually introduce any aliases and therefore doesn't have any tests for the new mechanism because our backend system uses a global table that isn't friendly to mocking for testing purposes. I've tested this manually using a placeholder alias to have confidence that it works, and I expect that a subsequent commit introducing the new "oracle_oci" backend will also introduce its "oci" alias and will include tests that cover use of the alias and migration from the alias to the canonical name and vice-versa. Signed-off-by: Martin Atkins <mart@degeneration.co.uk>